Albert w



A. W. HULL.

METHOD OF AND MEANS FOR AMPLIFYING ELECTRICAL VARIATIONS.

APPLICATION FILED NOV.8, I915- Patented Aug. 12, 1919.

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To all whom it may 00mm: Be i known thatjL-ALBERT W. HULL, a

citizen of the United States, residing at Schenectady, in the county of Schenectady, St-ate of .New York, haveiinvented certain new and useful Improvements-in Methods is to provide a means for amplifying-electri-- cal current, potential or energy'variations of such magnitude that they-cannot be readily measured or utilized toactuate-desired recording devices. l l

In carrying my invention into effect I connect a negative resistance device inparallel with a positive resistance and impress the current, potential or energy variations to be amplified upon the circuit in which the two resistances are connected, The total current flowing inthe circuit then will be the algebraic sum of the currents in the two resistances. If the two resistances are nearly pointed out with particularity-iii the 'ap-. pended claims. The invention itself, how-- ever, both as to its construction andmethod of operation together with further ob ects and advantages, will be's't'be understood by reference to the following description taken in connection with the accompanying draw:

ing in which Figure 1 shows one system of connections which may be devised in carrying my invention into effect. Fig. 2 shows a.

modification thereof, and Fig.3 shows the current characteristics of the system shown in Fig. 1.

In the arrangement shown in Fig. 1 a

positive resistance 1 or other device having positive resistance characteristics is connected in parallel wlth a.- negative resistance device 2.

sps te l ai Letters aw-f Q Patented Aug. Application neg i t ts: 8,1915. sedative-$00,401. V

either one of descriptionand claims 1' equal potenl- A photo-electric cell 3 isconnected in series with the two resistances: and the portion 13 of the battery 4 between:

f at was i7" and-18 is included in the Cir-- cuit to furnish current. .It is a well known characteristic of photo-electric cells that when an-electromotive force .is applied to their terminals and the cathode, which consists of potassium, sodium or other metal having the property "of emitting electrons under the influence of light, is subjected to .the'aotion of light,'. there will be a flow of negative electriclty'from the cathode to the anode "and this current will be proportional to the intensity of the light falling upon the cathode. The; current which is thus obtained,'however, is too small to be measured by ordinary measuringinstruments and the specific object of the arrangement hereshown is to provide a means for amplifyin this current to such a d that it can ily be measured or utilized for any desired purpose. Q

The negative resistance whichlwprefer to utilize in the present case is one Wh'lCh is de,-.- scribed and claimed in my prior'applimtion, Serial 1X0. 47,938, filed Au 30, 1915, and which consists of a high y evacuated envelop 5 provided-with a tungsten filament cathode 6 connected to leading-inaconduc-fl tors 7 for supplying current i'from the battery 8 for heating-it to incande'scence. This cathodeis I lindrical W'll'e grid Qwhich serves as an anode and which is connected to leading-in; wire 10; Surrounding the cathode and anode is a third electrode consistin of a. metaLcyIinder 11 connected-to lea -in-. wire I2. This cylinder is preferably. 311 1): close to the anode: The relative-positionsl of the=three electrodes maybe V&li6dz:ih? order to vary the operatingcharacteristics. of the device. The envelop 5 should prefer ably be exhausted to such a degree of-vacu-.- um. that when potentials Y of i the magnitude desired for the operation of the device. are

applied to the electrodes there. will :be no visible manifestations of gas ionization such as blue glow.

' ode no electrons will be received thereby. If,

however, a small positive potential is appliedto the thirdelectrodea portion of the ..elec-' preferablysurroundedby :1 cy- If a posi ive otential is impressed upon trons which .pass through the grid anode will;

g, r a strike =.it =and it will reccrve'a currentof negative electricity. The velocity w th which the. electrons will strike the th1rd elect-rode "will depend upon' the potentialfi tween it and the cathode. If this'potentl'al is increased the velocity will increase until the electronsstriking the third electrode are able by their impact to liberate secondary ing the third electrode will be attracted to the more positive anode. As the potential :isincreased a point will finally betreached at which the number of secondary electrons. leaving the third electrode is ust-equal to.

the number of primary electrons that; strike it. That is, each electron that-strikes libera'tes Iona-an average one secondary electron.

than the number of primary electrons received-and as a result the third electrode loses electrons, thereby. supplying current to the anode instead of-receivmg current,

These characteristics can hest be understood by-rei'erence to the 'curv-e-shownatA in F-ig. 3,'in--which-the ordinates represent the eiectron current fiowing to or away firomthe third electrodeand the abscissa represent the potential of the third electrade. part 0 B represents the-"increasing eicctron current reaching the third electrode "asthe potential is increased. When the potential'of the third electrode increases beyond that: corresponding to the point B, the-rate of "increase in the emission' of secondaryelectrons exceeds the'rate of increase in the primary-electrons received, and the: current hegins to decrease. When the potential of "the 'rfihild I electrode reaches thepoint-G' it loses as' many electrons as it receives and the current becomes zero. From C toD-thenumber of secondary electnbnsgivencfi continues to increase and :the' electron current from the electrode' to the anode increases. The point D is'fina'lly reached," however, at which the potential of the third electrode-so closely apcaches that of the *anode that the numer ofsecondary electrons losti'by the third electrode begins to decrease-because of the fact that the diii'erericeof potential between anode and third electrode is not great enough teat-tract asmanyr'electrons to the anode' as' hefore. This-continues until the point E is reached where the number of sec-- its potential as indicated by the part E F of the curve. The part B D of ;the current curve throughout'itlre greater portion of 1Zt,Sl l'1gl)l1 is approximately straight and the "where E is the potential of the third electrodell and R are constants, depending upon the characteristics of the particular device, and I is'the'electron current flowing to or away from the third electrode as isi'positive or negative. R corresponds to the resistance of an ordinary circuit except in this case it is a negative'resistance. Thus it will be seen that there is a certain range through which the device may be operated in 'Whichthe current received by the third electrode will vary inversely as the potential applied thereto. In the description which follows and in the claims the term negativeresistance is used to designate a device having this characteristic.

in the system shown in Fig. 1 battery 4- furnishes a constant potential for the anode 9. Theresistancos and the potential applied thereto are preferably so adjusted that when the photo-electriccell 3 is not illuminated and hence there is no current fiow-therethrough-there will be no current through either'resistance. This may be accomplished icy-connecting the end of the resistance into a point 17 in thebat-tery 4, so chosenthatthe potential thereby applied to the third 7 electrode 11 will correspond to the point C on the current curve. Since under tl eseconditionsno-current will flow through the-negative resistance there will not be 'anycurrent throughthe positive resistance. X Thecurrent through the positive resistance then under :operating conditions may 'berepresented by the straight line G which-falls? above or below the axis of ordinates, its-indicated; with'reversals in the potential applied thereto. The total current in the-circuit or the current in the photoelectric eell'willbe the algebraic-sum of the current through the two resistances. The algebraic sum ofthese two currents with vary-ing potenti-als on the third electrode is indicated by. the dotted lineH. By makingthe two resistances approximately equal to each'other in value so that the slope of curves-A and- G -i's approximately the same it will be seen that a very small change in the 'total current will cause a much greater change in the current through either of they two resistances and it will be apparent that the'degree of ampli-ficatioh which can thus be secured will depend upon how closely the two "resistances approach each other in 'vaiue.

When the photo-electric Cell i. not in fiucnced by any light source the portion 13 of battery at is open-oircuited in so far as its effect on the current through either resistance is concerned. When the photo-electric cell is illuminated by any light source current starts to flow therethrough and there is, in effect, a potential applied to both the negative'and positive resistances in parallel which is equal to .the potential of the portion 13 of the battery 4 less the drop in potential through the photo-electric cell. Since the current through the photo-electric cell varies in proportion to the intensity of the illumination thereon this drop in otential will vary in proportion to the intensity of the illumination. the application of this potential,- however, is not the same in both resistances. An inspection of the curves of Fi 3 will show that a change in potential om that corresponding to point. C will produce a current in one direction in the negative'rosistance and in the opposite direction in the positive resistance. Hence, it-will be apparent that the result of applying the potential mentioned to thetwo resistances will be to produce a current which circulates between the two resistances and which does not flow through the photo-electric celL. The currents in the .two resistances, however, will not be equal as the current in the resistance in which the current flows in the same direction as that in the photo-electric cell will be greater than the current in the other resistance by an amount equal to the current in the photo-electric cell. In other words the current through one of the resistances may be considered as made up of two parts; one part which flows through the photoelectric cell and one part which flows through the other resistance, while the current In the other resistance will be merely the current which circulates between the two resistances and does not pass through the photo-electric cell. It may be shown mathematically that the current through either resistance will bear substantially the same ratio to the current in the photo-electric cell that the value of the resistance bears to the difference between the two resistances.

' In other words, the current in the recording instrument 14 orother desired device which may be inserted in series with the resistance 1 will bearthe same ratio to the current in the photo-electric cell that the resistance 1 bears to the difference between the two resistances. This will be true irrespective of the nature of the current in rent. The same amplifying action will also take place if a source of alternating current is substituted for the photo-electric cell 3. If the current is alternating the currents The efiect of the photo-electric cell, that is, whether-it. is a constant current or a pulsating cur-' tion at the same timethat the total current reverses in direction as can .be seen from curves A, G and H. i

In the above description it has'been assumed that the total current in the circuit starts from zero orchanges in sign. It is not essential however that this should. be the case as the same princi le can equally well be applied to the ampli cation of small changes in unidirectional currents of relatively large magnitude, If the resistance 1 were connected, for example, to the same point inthe battery as the cathode 6 the current through the positive resistance would be as indicated by the curve K and the total current. in the circuit would follow 'the'curve L. If then the total current in the circuit had such a value that it fell on the portion of the curve where the resistance 2 is negative, changes in current would be 1 The form of my invention illustrated in Fig. 2 diflers'from that shown in Fig. 1 in that the photo-electricv cell is replaced by ,the secondary 15 of a transformer, the primany 16 of which may be supplied by a telephone current or any other variable current. which it is desired to amplify.

In the above description and in the claims which follow, I have used such expressions as current flow from cathode to. third elec-, trode to designate the net electron current received by the third electrode, or the current which will flow in the external circuit between cathode and third electrode. While I have. described the preferredembodiment of my invention it will be apparent that many changes therein may be made without departing from the scope of the appended claims. Forexample, in case it is desired to measure or utilize amplified potential variations the device for accomplishing the desired purpose is connected in shunt to the resistance 1 instead of in series therewith. It will also be apparent that the device 14 indicated may assume a great variety of forms in accordance with the purpose which is tobe accomplished.

What I claim as new-and desire to secure by Letters Patent of the United States, is

1. Means for amplifying electrical variations comprising a positive resistance and a negative resistance in parallel therewith, the two resistances being approximately equal to each other-in value.

2. Means for amplifying electrical variations comprising a device having positive resistance characteristics and a negative resistance .in parallel therewith, the two resistances being approxin'iately equal to each other, in value.

3. Means for amplifying electrical varia- 5 tions comprising a positive resistance, a

negative resistance, and means for supply- .ing the variations to be amplified to the two resistances in parallel.

4. Means for amplifying electrical variations comprising a negative resistance having a working range over which the current flow therethrongh varies inversely as the potential applied thereto, a positive resistance, and means for supplying the variations which are to be amplified to the two resistances in parallel.

5. Means for amplifying electrical variations comprising a negative resistance having an electron emitting cathode, and having a working range over which the current flow varies inversely as the potential applied thereto, a positive resistance and means for supplying the electrical variations to be amplified to the two resistances in parallel.

6. Means for amplifying electrical variations comprising a negative resistance having an electron emitting cathode, an anode and a third electrode inclosed in a highly evacuated envelop, and having a working range over which the current flow from the cathode to the third electrode varies inversely as the potential applied thereto, a positive resistance and means for supplying the electrical variations which are to be amplified to the two resistances in parallel.

7. Means for amplifying electrical variations comprising a negative resistance having an electron emitting cathode, an anode, and a third electrode near the anode and so positioned with respect to the cathode and anode that it will receive electrons from the cathode when it is more positive than the cathode, and so that secondary electrons given off from the third electrode can readily reach the anode, a positive resistance, and means for applying the electrical variations which are to "be amplified to the two resistances in parallel.

8. Means for amplifying electrical variations comprising a negative resistance, a positive resistance, and means for supplying electrical variations which are to be amplified to the two resistances in parallel, the two resistances being approximately equal to each other in value.

9. The method of amplifying electrical variations which consists in supplying variations which are to be amplified to a positive resistance and a negative resistance in parallel, and thereby producing amplified electrical variations in the positive resistance.

In witness whereof, I have hereunto set my hand this 6th day of November 1915.

ALBERT w, HULL. 

